The invention relates to a method and a device for utilizing alternative fuels in the production of clinker or cement.
Alternative fuels, as a rule, contain a number of elements whose combustion give rise to products, which can only be eliminated from the stream of exhaust gas by sumptuous steps of purification. Such products of combustion, such as for example sulfurdioxide can, however, risklessly be incorporated into the final product in the course of the production of clinker and cement so that along with the utilization of inferior fuels also the riskless disposition of products of combustion being troublesome in a conventional combustion is achieved at the same time. Alternative fuels, for instance formed by organic wastes, however, are characterized by a lower calorific value as compared to high value fuels. Temperatures of about 2000° C. have to be achieved by burners as employed for the heating of the rotary kiln in the production of clinker, whereby this is only achieved by using high value fuels such as gaseous or liquid fuels as well as, as the case may be, by using coal dust burners. Such burners have already been devised for the additional use of a portion of alternative fuels. Because of the relatively lower calorific value, these additions of fuels in the main burners of the clinker kiln result in many cases in an incomplete combustion and in perturbation of the flame of the actual high temperature burner. Compared to high value fuels, alternative fuels demand for a considerably longer holding time in the oxidizing atmosphere of the burner in order to safeguard complete combustion. Such a holding time cannot be ensured offhand at higher flow rates.
A substantial portion of the energy employed in the course of the production of clinker and cement is used for the calcining of the raw meal. The calcining is effected at substantially lower temperatures as compared to the clinker temperatures and, as a rule, is completely feasible at temperatures of about 850° C. The use of inferior and in particular of alternative fuels in connection with such a comparatively low temperature-level is theoretically conceivable. It is, however, problematic that in precalciners using the hot combustion gases of the clinker kiln such flow rates are prevailing that a sufficiently long holding or retention time respectively is ensured for the raw meal to be heated and being carried along afloat in the gas, but is not ensured for the complete combustion of lumpy alternative fuels.